Abstract
Coagulation in a flowing suspension is governed by the colloidal and hydrodynamic interactions between the aggregating particles and flocs, Beyond the initial particle-particle coagulation step these interactions determine the structure of a floe being formed, and at the same time they depend on the structure of the aggregating floes. To develop a better understanding of the coagulation process, we have examined both the internal structure and growth rate of floes formed by rapid shear coagulation of dilute suspensions. Floe sizes were measured by dynamic light scattering, and structure information was extracted from static light scattering spectra covering the domain 0.18<q.a<1.7, where q is the scattering wavenumber and a is the individual particle radius. Interestingly, comparison of the sheared suspension results with results for floes formed by Brownian coagulation reveals a similar structure for the two modes, indicating similar aggregation mechanisms act in both cases. In contrast, the growth kinetics for these two modes are inherently different, as expected. To model the growth behavior in a shear flow, we treat a porous floe as a body with a hydrodynamic radius which is less than the capture radius corresponding to floc-floc contact, and we compare predicted kinetics based on this model with data at several shear rates.